More than one-fourth of the honeybees in the United States have disappeared since last fall, and scientists are trying to figure out why.

By Jennifer Cutraro, 00:00 AM June 4, 2007

Entomologists—scientists who study insects—have a real mystery on their hands. All across the country, honeybees are leaving their hives and never returning.

It doesn't take long before a hive is nearly empty. Researchers call this phenomenon colony-collapse disorder. According to surveys of beekeepers across the country, 25 to 40 percent of the honeybees in the United States have vanished from their hives since last fall. So far, no one can explain why.